Redundant array of independent disks (RAID) is a storage technology that combines multiple storage devices into a single logical unit. Data can be distributed across the multiple storage devices in one of several ways called “RAID levels”, depending on what level of redundancy and performance is desired.
Common RAID levels implemented in storage systems include RAID 1, RAID 5, and RAID 6. In storage devices arranged as a RAID 1 array, an exact copy (or mirror) of each set of data is maintained on two storage devices, and in the event of a failure of one or the storage devices, the user data can be read directly from the remaining storage device in the RAID 1 array. In storage devices arranged as a RAID 5 array, a set of blocks storing user data and one corresponding block storing parity data are striped across three or more storage devices in the RAID 5 array, and in the event of a failure of one of the storage devices, the user data on the failed storage device can be reconstructed from the striped user data and parity data on the remaining storage devices in the RAID 5 array.
RAID 6 extends RAID 5 by adding one (or more) additional parity block(s). In other words, RAID 6 uses block-level striping with at least two parity blocks distributed across all the storage devices in the RAID 6 array. In the event of a failure of up to two of the storage devices in the RAID 6 array having two parity blocks, the user data on the one or two failed storage devices can be reconstructed from the striped user data and parity data on the remaining storage devices in the RAID 6 array.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.